Process for preparing benzoquinone

ABSTRACT

A PROCESS FOR PREPARING BENZOQUINONE BY OXIDIZING P-AMINOPHENOL WITH VANADIUM PENTOXIDE IN AN ACIDIC AQUEOUS SOLUTION, AND FOLLOWING RECOVERY OF THE BENZOQUINONE BY STEAM DISTILLATION, REGENERATING THE VANADIUM PENTOXIDE.

United States Patent O 3,708,509 PROCESS FOR PREPARING BENZUQUINONESamuel N. Holter, Penn Hills, Pa., assignor to Koppers Company, Inc. NoDrawing. Filed Nov. 15, 1971, Ser. No. 198,978

. Int. Cl. C07c 49/64 US. Cl. 260--396 R 4 Claims ABSTRACT OF THEDISCLOSURE A process for preparing benzoquinone by oxidizingp-aminophenol with vanadium pentoxide in an acidic aqueous solution, andfollowing recovery of the benzoquinone by steam distillation,regenerating the vanadium pentoxide.

FIELD OF THE INVENTION This invention relates to the preparation ofquinones from aromatic amines; more particularly to the oxidation ofp-aminophenol by vanadium pentoxide and, following product recovery,regenerating the vanadium pentoxide.

BACKGROUND OF THE INVENTION The oxidation of organic compounds hasreceived a fair amount of attention by those working in the art. Yet,the nature of the structure of organic compounds makes prediction ofoxidation mechanisms uncertain. There is even disagreement as to thedefinition of oxidation; it is generally agreed, however, that anydiscussion of oxidation involves (i) the loss of hydrogen from asubstance; (ii) the addition of oxygen to a substance; and (iii) theloss of electrons from a substance. A substance having the ability toeffect one or more of the foregoing changes upon an organic compound maybe termed an oxidizing agent or an oxidant.

In inorganic chemistry, the ability of a particular substance to oxidizeanother (i.e., oxidizing power) has been fairly well conceptualized.That is, in describing reactions of ionizable substances, a comparisonof the oxidizing power of different ions by reference to a standardresults in a measure of predictability. These concepts do not clearlyapply in organic chemistry.

Organic compounds are essentially covalent and the fission of thatcovalent bond is an essential feature of organic reactions. Thus, whileit may be known what structural change is necessary to transform oneorganic compound into another, the mechanism, the correct oxidant andthe process for effecting that change is usually highly uncertain. Suchis the case in the present invention.

DESCRIPTION OF THE PRIOR ART Benzoquinone has long been preparedcommercially by the oxidation of aniline with manganese dioxide and sul-Benzoquinone is easily reduced with iron and water to producehydroquinone o I OH [I OH which has wide application in the graphic artsas a photographic developer. Hydroquinone is also useful as anantioxidant and has found miscellaneous applications such as in dyes andmedicinals.

The known process for producing p-benzoquinone is disadvantageousbecause manganese sulfate is produced as a by-product, thereby creatinga waste disposal problem. Thus, an alternative, improved process forproducing hydroquinone has been sought.

It is known that benzoquinone can be formed by the oxidation ofaminophenols and diamines, because the intermediate quinonimines andquinonediimines are hydrolyzed rapidly in aqueous solution. However,suitable processes and effective oxidants to produce benzoquinone inhigh yield from starting materials of that type were not known prior tothe present invention.

It has been discovered that p-aminophenol can be oxidized by apentavalent vanadium compound, preferably vanadium pentoxide, to producebenzoquinone:

O OH I M SUMMARY OF THE INVENTION The present invention provides aprocess for preparing benzoquinone comprising: contacting a suspensionof vanadiurn pentoxide in an acidic aqueous solution of p-aminophenol toform a reaction mixture; and recovering benzoquinone from the reactionmixture. The present invention further provides that the recovery of thebenzoquinone product includes distilling benzoquinone from the reactionmixture and thereafter heating the residue of the reaction mixture inthe presence of oxygen, preferably to a temperature of at least 400 C.,to regenerate the vanadium pentoxide.

More specifically, the present invention provides a process foroxidizing p-aminophenol to produce benzoquinone comprising the steps of:adding an aqueous solution of p-aminophenol to a suspension of vanadiumpentoxide in an acidic aqueous solution to form a reaction mixture;continuously passing steam through the reaction mixture so formed duringthe addition of the p-aminophenol solution to recover benzoquinonetherefrom; and heating the residue of the reaction mixture in thepresence of oxygen following the addition step to regenerate thevanadium pentoxide.

The term regenerate as used herein means to restore the spent vanadiumresidue to its initial statevanadium pentoxide.

DETAILED DESCRIPTION OF THE INVENTION Preparation of p-aminophenolp-Aminophenol has been prepared by a variety of methods. The oldertechniques include the reduction of p-nitrophenol by either catalytichydrogenation or the use of reducing agents. More recently,p-aminophenol has been prepared by the reduction of nitrobenzene (i)with aluminum in acid solution; (ii) electrochemically in acid solutionin the presence of stannous salts; and (iii) by hydrogenation in thepresence of a catalyst such as platinum on carbon and platinum sulfidecombined with a simultaneous rearrangement of the intermediate, N-phenylhydroxylamine.

Example 1 below describes a method for preparing paminophenol in arocking autoclave by catalytic reduction of nitrobenzene in the presenceof sulfuric acid. Aniline was also obtained under the conditions setforth there. Other runs made in accordance with the procedures ofExample I are tabulated in Table A.

EXAMPLE I A glass liner to fit a 2.4 liter rocking autoclave was chargedwith 12.3 g. (0.1 mole) nitrobenzene (Fisher Certified), 12 g.concentrated sulfuric acid in 300 ml. of water and 1.0 g. sulfided 5%Pt/C. The hydrogenation was performed at 125 under 500 p.s.i. ofhydrogen.

After hydrogen uptake had ceased, the catalyst was removed by filtrationand the filtrate made alkaline with concentrated ammonium hydroxide (PH9). Upon becoming alkaline, the solution immediately became dark in thepresence of air. The alkaline solution was extracted with 12x 250 ml.portions of ether. The ether extract was dried over magnesium sulfate,filtered, and evaporated on a steam bath to afford a residue of 7.9 g.The residue was washed with 100 ml. of benzene to yield 4.2 g. ofp-aminophenol. The filtrate from the benzene wash was evaporated toyield 1.9 g. of aniline.

p-Aminophenol produced in this manner for subsequent oxidation tobenzoquinone should be substantially free of aniline to avoid reducedproduct yields.

The product of the reduction of nitrobenzene will generally contain asmall amount of o-aminophenol. However, the presence of this isomer inamounts up to about 4% probably will have no adverse effect upon theyields obtained with the present invention.

4 significant decrease in yield has been observed with ratios up to20:1. V O /p-aminophenol ratios above that range will involve largevolumes of water since the V 0 is held in suspension and this imposespractical limitations upon the process.

The oxidation reaction is carried out in an aqueous solution containinga strong, preferably nonvolatile, acid such as sulfuric acid. The acidconcentration is not critical although p-benzoquinone is unstable in thepresence of strong acid; therefore the concentration of acid should notexceed about 0.12 molar in order to obtain good yields of benzoquinone.

The reaction is preferably carried out by adding an aqueous solution ofp-aminophenol to a suspension of V 0 in an acidic aqueous solution.Reverse addition procedures may be used, however, to carry out theprocess. The presence of strong acid improves product yield; however, aportion of the total acid used may be contained in the p-arninophenolstarting solution without adverse effects.

The possibility of side-reactions between the reactants and thebenzoquinone formed by the reaction makes it desirable to continuallyremove product from the reaction mixture as it is formed. This isaccomplished by vigorously passing steam through the reaction mixtureduring the addition of p-aminophenol thereby distilling oil? thep-benzoquinone product. Under these conditions, the temperature of thereaction mixture is maintained at about 100C. However, it is believedthat the process of the invention can be carried out below 100 C. byoperating under reduced pressure. Operation at temperatures above 100 C.is also believed possible in appropriate pressure apparatus. Obviously,however, economic considerations makes it desirable to operate theprocess at atmospheric pressure.

A unique advantage of the present invention is the ability to regeneratethe oxidant by heating the solids from the reaction mixture in anoxidizing atmosphere. The regeneration step may be performed by eitherfiltering the residual solids from the reaction and heating them in airor by heating the residue of the reaction in the reaction vessel underpressure in the presence of oxygen. Recovery of V 0 by the lattertechnique of regenerating the V 0 TABLE A p-Amino- Nitrophenol, Amlin,benzene, Catalyst, Temp., Pressure, percent percent m as H2504 g. C.lb./in. yield yield 0. 1 12 g./300 ml. H20 1. 0 110 500 35 0. 1 12g./300 ml. H20 1. 0 95 500 29 22 0. 1 12 g./300 ml. H20 1. 0 80 500 38 02 12 g./300 ml. H10 1. 0 125 500 33 I2 I 5% PtS/C.

Preparation of benzoquinone The preferred starting material for use inthe present invention is p-aminophenol. It is believed, however, thatother compounds may also be oxidized according to the present inventionto produce quinones; these compounds include the diamines, analogs ofp-aminophenol, and methyl-substituted derivatives of p-aminophenol andthe diamines.

According to the invention, the p-aminophenol is oxidized by apentavalent vanadium compound, preferably vanadium pentoxide. The molarratio of V 0 to paminophenol in the reaction should be maintained at insitu offers particular advantages in time-saving and equipment costsbecause no external filtration and evaporation steps are required.Regeneration of V 0 according to the invention has been shown to becomplete and little, if any, loss of activity in the regenerated V 0 hasbeen observed.

The temperature required for regeneration is about 400 C. Highertemperatures may be employed but care must be exercised to not reach thefusion temperature of V 0 which is about 50-70 C. below its meltingpoint.

The present invention may be illustrated by reference to thenon-limiting examples which follow. All percentages about 4:1 or aboveto achieve good product yields. No are by weight unless otherwisestated.

5 EXAMPLE n A 1-1. three-necked flask-arranged for. steam distillationand equipped with an addition funnel and magnetic stirrer was chargedwith90.9 'g. (0.5 mole) vanadium pentoxide It has been found thattechnical grade V unused or regenerated, gives yields of benzoquinonecomparable to purified V 0 ,As stated above, the vanadium'pentoxide canbe re- (Fisher Certified)5.9 g. (0.06 mole) concentrated sulfuric 5generated in an aqueolls lf' i Thus} i believed a id d 300 1 of t ASolution f 09 v (OJ mole) that-the process of the invention issusceptible of continuf p aminophenol in 200 mL water was prepared byous operation under oxygen .pressure. If, however, a conheating toapproximately 90 and then transferred to the tmuous B Is not d bl aCYCIIC lQ P c ss c addition funnel which was heated by means of -aheating used Whlch tht? OXIdatIOH 0f pp q 15 tape. The solution ofp-aminophenol was added dropwise 10 rled- Q1 a 'f followed y.regenfifatlon of tha to the reaction flask while steam was vigorouslypassed vanadlum Pelltoxlde 1n i Same l'eactor- Example 111 into theflask. The addition required approximately 2.5 below tionfifms thefofegolnghours. The distillation was continued until the distillateEXAMPLE HI was colorless. The distillate was then extracted with 100 ml.portions of benzene until no further color was im- 5 A Tockmg*jultoclave f pp Wlth a glass parted to the benzene. A yield of 8,3 g.(77%) of quinone llner a charged Wlth pp t y 400 f n agil was obtained.The contents of the reaction flask were 0115 suspenslPn 9 reducedvfinadlum Compounds Obtained filtered to remove water insolublematerial. The solids from oxldatlon P-Q P The qutoclave Was were h h t dt 600 t i 883 97%) f pressured to 500 p.s.r. with oxygen at ambienttemperad V 0 ture and then heated to approximately 300 C. The tem-Additional runs were carried out in accordance with the Pefatufe 9maintained at C. for 1.3 hrs. with a procedures of Example II and theyare reported in Table corresponding pressure of 1710 p.s.i. Upondischarge of B belo the autoclave, it was observed that the originaldark green TABLE B p-Amlno- Y Benzoqui- V20 phenol, Oxidant, H2804,none, perpercent moles oxidant moles moles cent yield recovery Remarks0.1 V205 0. 5a 0. 06 31 0.1 V505 0.5 0. 06 98 pH 7' 0.1 v50 0.5 0.05 4497 H7 0.1 V105" 0.5 0. 06 77 100 As KHSO:

0.05 V50 0.5 0.06 81 95 H? 0.05 V205 0.5 0. 06 85 76 pH3 0.05 V105 e 0.50. 06 98 98 pH 4 0.05 v20, u 0.5 0. 06 91 88 G. 0.05 V205 0.5 0.06 89 91pH 2 0. 05 V205 b 0. 5 43 99 0.05 vzoi 0.5 0.03 29 96 117 I Technicalgrade V10 treated with con 0. NHO Purified V50 (99.9%). 9 Purified V505regenerated. d Purified V205 regenerated two times. Recovery based onwater insoluble material only. Adjusted reaction mixture to pH indicatedberfore filtration. I Added 20 ml. cone. NHO; to hot reaction mixturebefore filtration.

The results of Run N0. 10 indicate that some acid in the solids hadchanged to golden yellow. Chemical analysis reaction mixture isnecessary in order to obtain good of the yellow solids showed thepresence of vanadium yields of benzoquinone. The table also shows thatrepentoxide but no reduced vanadium compounds. covery of the vanadiumpentoxide is not affected aP- What is claimed is: preciably by the pH ofthe reaction mixture before filtra- 1. A process for preparingbenzoquinone comprising: tion. The V 05 was regenerated at 400 insteadof 600 (A)v contacting a suspension of vanadium pentoxide used inExample H and thereby avoided the possibility of in an acidic aqueoussolution with an aqueous solufusion of the V 0 tion of p-aminophenol ata temperature of about Table C below reports runs carried out inaccordance 0 100 C. and at about atmospheric pressure, the molar withthe procedures of Example I and illustrates the eifect ratio of vanadiumpentoxide to p-aminophenol beon the yield of benzoquinone of decreasingthe V O ing maintained at about at least 4:1, to form areacp-aminophenol mole ratio. tion mixture; and

TABLE 0 (B) recovering said benzoquinone from said reaction Baummixture. p-Aminoinone, 2. A process as recited in claim 1 wherein saidrecovery figfg X295 g 221 3 includes: distilling benzoquinone from saidreaction mixture and thereafter heating the residue of said reaction Runnumb r: 0' 025 J 0. 015 (b mixture in the presence of oxygen toregenerate said vana- 0. 05 0. 5' 0.015 as 96 70 drum pentoxide. 8:8 :328 8%? 3g 98 3. A process for preparing benzoquinone comprising 0.125 0.50. 0a 76 95 the steps of:

Q25 15 27 (h) (A) adding an aqueous solution of p-aminophenol to asuspension of vanadium pentoxide in an acidic aqueous solution, themolar ratio of vanadium pentoxide to' p-aminophenol being maintained atabout at least 4:1, to 'formareactio'n mixture; '(B) continuouslypassing steam through said reaction mixture during said addition torecoverbenzoquinone therefrom; and (C) heating the residue of thereaction mixture in the presence of oxygen following thehddition step'toregeneratesaid vanadium pen'toxide. 4. A process as recited in clairn3wherein? said resid 400 C.

ue is 'heated' to a temperature of at' least 10 References lit ed UNITEDSTATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORREC'HONPatent No. 3,708,509 Dated January 2 .1973

Inventor) Samuel N. Holter It is certified that error appears in theabove-identified patent and that said Letters Patentare hereby correctedas shown below:

Colunm 3, Table A, Last Heading, Anilin," should read ----Aniline,----;

Column 5, Table B, Footnote a, "NHO3" should read Column 5, Table B,Footnote g, "NHO should read Column 5, Table C, Under Heading V 0percent recovery", "96" should read -99--.

Signed and'sealed this 22nd day of May 1973 (SEAL) Attest:

EDWARD, M.FL ETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM po'wso (10459) USCOMM-DC eoave-pes fi U.S. GOVERNMENTPRINTING OFFICEz 1969 0-366-334.

